This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. PRMTs (Protein Arginine Methyltransferases) are an important family of enzymes that regulate many biological processes via methylation of protein arginine residues. However, their biochemistry and structural biology are poorly characterized. Furthermore, of the 3 xray crystal structures of PRMTs available, none have cofactors or substrates present. We have produced highly purified and enzymatically active Xenopus laevis PRMT5 complexed with its WD40 repeat cofactor, MEP50. Our proposed SAXS studies on this protein complex will test our hypothesis that MEP50 serves as a ?substrate presenter? for the PRMT5 enzyme. We request rapid access as we are preparing a publication on the biochemistry of PRMT5 and we would be excited about including SAXS studies in this manuscript.